The present invention relates to a device mounting method, and particularly to a technique of mounting micro-semiconductor devices, which have been cut from a wafer, in a matrix array on a circuit board. More specifically, the present invention concerns a technique of producing an image display by two-dimensionally arraying light emitting diodes on a circuit board.
FIG. 11A is a schematic perspective view showing one example of an image display used for a flat type TV set. As shown in this figure, wiring portions 108 and extraction electrodes 108a for external connection are formed on the surface of a circuit board (mounting board) 7 typically made from alumina. Some of the wiring portions 108 are taken as pad electrodes, and light emitting diodes (LED chips) are fixed on the pad electrodes by die-bonding.
FIG. 11B is a schematic partial sectional view of the image display shown in FIG. 11A. As shown in this figure, the surface of the circuit board, excluding the wiring portions 108 and the extraction electrodes 108a, is covered with a black resin 123. The LED chip has a P/N junction layer. A pad electrode 122 is formed on the top of each of the LED chips. The pad electrodes 122 of the LED chips are electrically connected to the extraction electrodes 108a by wire bonding using fine wires 120. When a current is supplied to each of the LED chips with the pad electrode 122 taken as the positive side and the wiring portion 108 taken as the negative side, the P/N junction layer of the LED chip emits light, resulting in a desired display.
In general, semiconductor devices such as LED chips are formed on wafers by using a semiconductor fabrication process. In this case, the number of chips to be formed on each wafer becomes larger as the size of the chips becomes finer. The sizes of LED chips have been reduced to a level of, for example, 20 μm×20 μm. On the other hand, in some applications of image displays, the tendency toward higher definitions and larger sizes of the image displays has been increased. Typically, there has been already realized a plasma display of a type in which pixels of the number of about four millions are formed on a display board having a diagonal dimension of 50 inches. Such production of a plasma display, however, has a problem that the work of accurately arraying a large number of, for example, several millions of individual micro-devices, such as LEDs, of a size of about 20 μm×20 μm on a mounting board having a diagonal dimension of 50 inches, takes a lot of labor and also a lot of working time on the basis of the existing mounting technique. To cope with such a problem, various methods have been proposed; however, any one of the methods seems to reach the practical level. For example, U.S. Pat. Nos. 5,783,856 and 5,824,186 have disclosed a technique of providing a large number of recesses in a mounting board at positions where chips are to be arrayed, wherein micro-chips are automatically fitted in the recesses by making use of a fluidic motion; however, such a method is not necessarily effective for a device which cannot neglect not only positions but also orientations of the chips to be mounted. Japanese Patent Laid-open No. Sho 56-17385 has proposed a technique of repeating transfer of chips so as to move the chips from a wafer side to a mounting board side; however; this document does not disclose any concrete means for efficiently arraying micro-chips on a large-sized mounting board.